Compressor Surges of Near-resonant Type and Convective Type; the Boundaries and the Differences in the Behaviors

Compressor deep surges are observed to be of either near-resonant type or convective type. The differences of the behaviors and the boundaries between both types were tried to make clear in the situations of a single-stage axial compressor on the basis of numerical-experimental results by use of a surge simulation code. In the near-resonant surges, the surge frequencies relative to the resonance frequency range roughly from 0.9 to 1.1, close to the resonance condition. The surges tend to degenerate just above or in the resonance range. The convective type is said to perform actions of emptying and filling the flow in the delivery plenum, showing lower relative surge frequencies less than 0.9. The study for the criteria governing the boundary between both surge types has suggested an axial motion parameter as the candidate. The convective surges are observed to occur above the boundary value of the axial motion parameter. In the environment, the fluctuation amplitudes tend to be larger than those in the near-resonant surges. The situations force the compressor to work over a wider range from the turbine-action zone to the deeply-reverse flow zone along the stage characteristic. The flow reversals thus reinforced will enhance the so-called emptying and filling actions in the convective surges.